Lacosamide, chemical name: (R)-N-benzyl-2-acetamido-3-methoxypropionamide, CAS number: 175481-36-4, has a structural formula shown below:

Lacosamide is a medication for treating epilepsy and neuropathic pain developed by Schwarz biosciences in Germany, and is used for the adjunctive treatment of partial-onset epilepsy in 16 years old or older patients with or without secondary generalized seizures. Lacosamide, also referred to as erlosamide, has an action mode different from that of all the current commercially available antiepileptic drugs: lacosamide regulates the activity of sodium channels, while other commercially available antiepileptic drugs block the sodium channels. The sodium channels play a vital role in adjustment of nervous system activity for nerve cell communication. Sometimes, abnormal hyperactivity of the sodium channel may cause seizures of epilepsy. Therefore, the action mode of lacosamide is considered as to reduce the hyperactivity of the sodium channels, and the motion of adjusting nerve cells may control the seizures of epilepsy. Clinical studies also indicate that, lacosamide is bound to collapse response mediator protein-2 (CRMP-2, mainly distributed in phosphoprotein in the nervous system for neurounal differentiation and for controlling axonal overgrowth), and lacosamide is the unique antiepileptic drug on the market that interacts with CRMP-2.
In U.S. Pat. No. 6,048,899 (patentee: Research Corporation Tech., Inc., publication date: Apr. 11, 2000), Lacosamide is first reported, and the preparation process is shown below:
Route one:

where the group -Cbz specifically is benzyloxycarbonyl, that is,

Note: the group -Cbz in the following structures and specifications are as defined above.
In this route, two critical intermediates, that is, Compound 2 and Compound 3 are involved:

In the preparation of lacosamide through the reactions mentioned above, iodomethane and silver oxide that are cost expensive need to be used, which is not beneficial to industrial production; and moreover, in deprotection of the group Cbz, a Pd—C catalyst is used, and the production cost is high.
In U.S. Pat. No. 6,048,899, another route, that is, Route two, is disclosed:

The difference between Route two and Route one lies in that, Compound 1 is subjected to an alkylation reaction; next, Compound 6 is subjected to a condensation reaction, to obtain Compound 3. It can be found through comparison with Route one that, the order of the alkylation reaction and the condensation reaction is reverse. The common features of the two routes are that: reagents and methods used in the alkylation reaction and the condensation reaction are substantially the same; during the reactions, a benzyloxycarbonyl group is used to protect the amino group, so a process of protection of the benzyloxycarbonyl group and a process of deprotection of the benzyloxycarbonyl group are involved, and the methods corresponding to the two steps are the same; and finally, the methods for preparing lacosamide from Compound 4 are the same. Therefore, it can be seen that, during the preparation of lacosamide, the order of the alkylation reaction and the condensation reaction and the step and method for protecting the amino group are very important.